1. Field of the Invention
The present invention relates to a process to increase the cetane rating of distillate and diesel boiling range fractions.
2. Description of the Related Art
The use of membrane separation processes to divide feed streams into permeate streams and retentate streams of different chemical composition is well known in the art.
The removal of aromatic hydrocarbons from feed streams containing mixtures of aromatic hydrocarbons and non-aromatic hydrocarbons using membranes is a desirable process which has been described in the patent literature.
U.S. Pat. No. 2,947,687 teaches the separation of hydrocarbons by type through a non-porous membrane using a membrane solvent to enhance the permeation rate. Membrane solvents include substituted hydrocarbons which are soluble in and have solvent power for the permeate of the membrane. The hydrocarbon solvent is an organic compound containing one or more atoms of halogen, oxygen, sulfur or nitrogen. Thus, materials such as carbontetrachloride, alcohols, ketones, esters, ethers, carboxylic acids, mercaptans, sulfides (e.g., diethylsulfide, etc.), nitropropane, nitrobenzene, acetonitrile, formamide, ethylene diamine, etc. may be employed in an amount ranging from 1 to 100% based on total solvent to hydrocarbon feed. The process may be operated at a pressure differential between the feed and permeate zone with a permeate being removed by vacuum. Alternately, the permeate can be removed by a sweep stream such as steam, air, butane, etc.
The membrane is non-porous and includes natural or synthetic rubber, vinyl polymers, cellulose esters, cellulose ethers.
The process can use any hydrocarbon source as feed and the separation achieved is in the order: saturated hydrocarbons, <unsaturated hydrocarbons, <aromatics. Saturated hydrocarbons of approximately the same boiling range permeate in the order of increasing selectivity: branched chain, <cyclic-chain, <straight chain configuration; i.e., straight chain paraffins more readily permeate through the membrane.
U.S. Pat. No. 3,140,256 teaches a membrane separation process employing a membrane comprised of a cellulose derivative (e.g., cellulose ester or ether) modified by reaction with aldehydes, organic diisocyanate, organic monoisocyanate, organo-phosphorus chlorides and organo-sulfur chlorides. Hydrocarbon feeds can be separated into these components by type using the membrane; e.g., aromatics can be separated from unsaturated hydrocarbon (olefins or diolefins) and/or from paraffins, or branched chain aliphatic hydrocarbons can be separated from other aliphatic hydrocarbons which have a different number of branched chains. Aromatic hydrocarbons permeate more rapidly than do the saturated (i.e., paraffinic) hydrocarbons. In an example, methyl cyclohexane permeated through the membrane more selectively than did isooctane.
U.S. Pat. No. 3,370,102 teaches the membrane separation of aromatics from saturates in a wide variety of feed mixtures including various petroleum fractions, naphthas, oils, and other hydrocarbon mixtures. Expressly recited in '102 is the separation of aromatics from kerosene. The process produces a permeate stream and a retentate stream and employs a sweep liquid to remove the permeate from the face of the membrane to thereby maintain the concentration gradient driving force. U.S. Pat. No. 2,958,656 teaches the separation of hydrocarbons by type; i.e., aromatics, unsaturated, saturated by permeating a portion of the mixture through a non-porous cellulose ether membrane and removing permeate from the permeate side of the membrane using a sweep gas or liquid. Feeds include hydrocarbon mixtures (including virgin naphtha, naphtha from thermal or catalytic cracking, etc.) U.S. Pat. No. 2,930,754 teaches a method for separating hydrocarbons by type; i.e., aromatics and/or olefins from gasoline boiling range mixtures by the selective permeation of the aromatics through certain cellulose ester non-porous membranes. The permeated hydrocarbons are continuously removed from the permeate zone using a sweep gas or liquid. U.S. Pat. No. 4,115,465 teaches the use of polyurethane membranes to selectively separate aromatics from saturates via pervaporation.
Polyurea/urethane membranes and their use for the separation of aromatics from non-aromatics are the subject of U.S. Pat. No. 4,914,064. In that case the polyurea/urethane membrane is made from a polyurea/urethane polymer characterized by possessing a urea index of at least about 20% but less than 100%, an aromatic carbon content of at least about 15 mole percent, a functional group density of at least about 10 per 1000 grams of polymer, and a C═O/NH ratio of less than about 8.0. The polyurea/urethane multi-block copolymer is produced by reacting dihydroxy or polyhydroxy compounds, such as polyethers or polyesters having molecular weights in the range of about 500 to 5,000 with aliphatic, alkylaromatic or aromatic diisocyanates to produce a prepolymer which is then chain extended using diamines, polyamines or amino alcohols. The membranes are used to separate aromatics from non-aromatics under perstraction or pervaporation conditions.
Thin film compositions can be prepared either from suspension deposition as taught in U.S. Pat. No. 4,861,628 or from solution deposition as taught in U.S. Pat. No. 4,837,054.
The use of polyurethane imide membranes for aromatics from non-aromatics separations is disclosed in U.S. Pat. No. 4,929,358. The polyurethane-imide membrane is made from a polyurethane-imide copolymer produced by end capping a polyol such as a dihydroxy or polyhydroxy compound (e.g., polyether or polyester) with a di- or polyisocyanate to produce a prepolymer which is then chain extended by reaction of said prepolymer with a di- or polyanhydride with a di- or polycarboxylic acid to produce a polyurethane/imide. The aromatic/non-aromatic separation using said membrane is preferably conducted under perstraction or pervaporation conditions.
A polyester imide copolymer membrane and its use for the separation of aromatics from non-aromatics is the subject of U.S. Pat. No. 4,946,594. In that case the polyester imide is prepared by reacting polyester diol or polyol with a dianhydride to produce a prepolymer which is then chain extended preferably with a diisocyanate to produce the polyester imide.
U.S. Pat. No. 4,929,357 is directed to non-porous isocyanate cross-linked polyurethane membranes. The membrane can be in the form of a symmetric dense film membrane. Alternatively, a thin, dense layer of isocyanurate cross-linked polyurethane can be deposited on a porous backing layer to produce a thin film composite membrane. The isocyanurate cross-linked polyurethane membrane can be used to separate aromatic hydrocarbons from feed streams containing mixtures of aromatic hydrocarbons and non-aromatic hydrocarbons, the separation process being conducted under reverse osmosis, dialysis, perstraction or pervaporation conditions, preferably under perstraction conditions.
U.S. Pat. No. 4,962,271 teaches the selective separation of multi-ring aromatic hydrocarbons from distillates by perstraction. The multi-ring aromatics are characterized by having less than 75 mole % aromatic carbon content. Perstractive separation is through any selective membrane, preferably the aforesaid polyurea/urethane, polyurethane imides or polyurethane isocyanurates.
U.S. Pat. No. 4,990,275 relates to a copolymer composition comprising a hard segment of a polyimide and a soft segment of an oligomeric aliphatic polyester. Membranes made from the copolymer are useful for aromatic/saturates separations. The polyimide is derived from a dianhydride having between 8 and 20 carbons and a diamine having between 2 and 30 carbons while the oligomeric aliphatic polyester is a polyadipate, polysuccinate, polymalonate, polyoxalate or polyglutarate.
U.S. Pat. No. 4,962,270 teaches the improved separation of feed streams containing multiple components affected by means of a multi-membrane staged pervaporation process wherein each membrane stage in series is run at progressively higher temperature, stronger vacuum or both than the preceding stage. This process is especially useful for separating components from wide boiling range mixtures. The separation of a multi-component feed mixture of aromatic hydrocarbons and non-aromatic hydrocarbons is specifically mentioned.
U.S. Pat. No. 5,095,171 teaches that the separation of aromatic hydrocarbons from mixtures of aromatic and non-aromatic hydrocarbon feeds under pervaporation conditions is improved by the control of the amount of oxygen present in the feed. The amount of oxygen in the feed, such as heavy cat naphtha or other cracked feed, should be less than 30 wppm, preferably less than 10 wppm. The oxygen level in the feed can be controlled by the addition of small amounts of oxygen scavenger into the feed. Hindered phenols are representative of useful oxygen scavengers. Hydrocarbon feeds which can be subjected to the control of oxygen content include any cracked feed including by way of example light cat naphtha, intermediate cat naphtha, heavy cat naphtha, jet fuel, diesel fuel, coker gas oil, in general any cracked stock boiling in the 65° to 1050° F. range.
U.S. Pat. No. 5,098,570 is directed to a multi-block polymeric material comprising an urea prepolymer chain extended with a second compatible prepolymer selected from the group of prepolymers comprising (a) an (A) dianhydride or its corresponding tetraacid or diacid-diester combined with a monomer selected from (B) epoxy, diisocyanate, polyester, and diamine in an A/B mole ratio ranging from about 2.0 to 1.05, preferably about 2.0 to 1.1, and (b) an (A) diamine combined with a monomer selected from (B) epoxy and dianhydride or its corresponding tetraacid or diacid-diester in an A/B mole ratio ranging from about 2.0 to 1.05, preferably about 2.0 to 1.1, and mixtures thereof. It is also directed to membranes of the above-recited multi-block polymeric material, especially membranes comprising them, dense films of said multi-block polymeric material deposited on a microporous support layer producing a thin film composite membrane. The membranes of the multi-block polymeric material, especially the thin film composite membranes, are useful for separating aromatic hydrocarbons from mixtures of same with non-aromatic hydrocarbons under perstraction or pervaporation conditions.
U.S. Pat. No. 5,130,017 is directed to a multi-block polymeric material comprising a first amide acid prepolymer, made by combining (A) a diamine with (B) a dianhydride or its corresponding tetraacid or diacid-diester in an A/B mole ratio ranging from about 2.0 to 1.05, preferably about 2.0 to 1.1, chain extended with a second, different, compatible prepolymer selected from the group of prepolymers comprising (A) a dianhydride or its corresponding tetraacid or diacid-diester combined with a monomer selected from (B) epoxy, diisocyanate and polyester in an A/B mole ratio ranging from about 2.0 to 1.05, preferably about 2.0 to 1.1.
It is also directed to membranes of the above-recited multi-block polymeric materials, especially membranes comprising thin, dense films of said multi-block polymeric material deposited on a microporous support layer producing a thin film composite membrane.
The membranes of the multi-block polymeric material, especially the thin film composite membranes, are useful for separating aromatic hydrocarbons from mixtures of same with non-aromatic hydrocarbons under perstraction or pervaporation conditions. Suitable feed streams for aromatics from saturates separation are heavy cat naphtha, intermediate cat naphtha (200-320° F.), light aromatics content streams boiling in the C5-300° F. range, light catalytic cycle oil boiling in the 400-650° F. range, reformate streams as well as streams in chemical plants which contain recoverable quantities of benzene, toluene, xylene (BTX) or other aromatics in combination with saturates.
U.S. Pat. No. 5,221,481 is directed to a multi-block polymeric material comprising an ester prepolymer chain extended with a second, different, compatible prepolymer selected from the group of prepolymers comprising (a) an (A) dianhydride or its corresponding tetraacid or diacid-diester combined with a monomer selected from (B) epoxy, diisocyanate, polyester, and diamine in an A/B mole ratio ranging from about 2.0 to 1.05, preferably about 2.0 to 1.1; and (b) an (A) diamine combined with a monomer selected from (B) epoxy, diisocyanate, and dianhydride or its corresponding tetraacid or diacid-diester in an A/B mole ratio ranging from about 2.0 to 1.05, preferably about 2.0 to 1.1, and mixtures thereof. It is also directed to membranes of the above-recited multi-block polymeric materials, especially membranes comprising thin, dense films of said multi-block polymeric material deposited on a microporous support layer producing a thin film composite membrane. The membranes of the multi-block polymeric material, especially the thin film composite membranes, are useful for separating aromatic hydrocarbons from mixtures of same with non-aromatic hydrocarbons under perstraction or pervaporation conditions.
U.S. Pat. No. 5,290,452 is directed to a polyester/amide membrane, its preparation and its use for organic liquid separation. The polyester/amide membrane is made by reacting a dianhydride with a polyester diol in a 2:1 to 1.05:1 mole ratio to end cap the diol to produce a prepolymer which is reacted with excess thionyl chloride to convert all of the unreacted anhydride and all carboxylic acid groups to acid chloride groups. The resulting acid chloride derivative is dissolved in organic solvent and interfacially reacted with a diamine dissolved in an aqueous solvent. The excess solutions are removed and the resulting thin film membrane is dried. The membranes are useful for organic liquid separations, especially the separation of aromatic hydrocarbons from mixtures of same with non-aromatic hydrocarbons, preferably under perstraction or pervaporation conditions.
U.S. Pat. No. 5,416,259 teaches that the pervaporative treatment of hydrocarbon feeds which have been exposed to air or oxygen and which contain mixtures of aromatic and non-aromatic hydrocarbons to selectively separate the feed into an aromatics-rich stream and a non-aromatics-rich stream is improved by the step of pretreating the hydrocarbon feed over an adsorbent such as attapulgite clay.
U.S. Pat. No. 5,635,055 teaches that the yield and quality of products secured from cracking units is increased by the process of subjecting the product stream secured from such cracking unit to a selective aromatics removal process and recycling the recovered aromatics lean (saturates-rich) stream to the cracking unit whereby such saturates-rich stream is subjected to increased conversion to higher value desired products.
U.S. Pat. No. 5,643,442 is directed to a process whereby distillate or hydrotreated distillate effluent is separated into an aromatics-rich permeate and an aromatics-lean retentate by use of a permselective membrane with the aromatic-rich permeate being sent to a hydrotreater, thereby increasing the quantity of reduced aromatics content product. The aromatics-lean retentate can be sent downstream and blended into the jet fuel, heating oil or diesel pool.